Get PackageManager on demand in ActivityStarter.

PackageManager may not be ready by the time ActivityStarter is
created. As a result we cannot pass it in as an argument at
construction time. This changelist addresses this by adding an
accessor in ActivityManagerService, which fetches the service
on demand.

Change-Id: I117af29170cc70198072908da1d728d4e9317e46
Fixes: 69550166
Test: cts/tests/framework/base/activitymanager/util/run-test CtsVoiceSettingsTestCases android.voicesettings.cts.AirplaneModeTest